Hardened metallic structure



J I A A 5 a 1 1 Howard E Somes' I A 7' TORNE Y Patented Feb. 13, 1951 nannnmsn mn'ramo s'rnucrrma Howard E. Somes, Detroit, Mich assllnor, by mesne assignments, to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Application October 27, 1943, Serial No. 507,784

I zclaims.

This invention relates to hardened metallic structures and particularly to tubular structures adapted to withstand sudden loads and high pressures.

) An object of this invention is to provide a metallic structure, which is particularly adapted for use in tubing form, of such structural characteristics as provide an article of great resistance to suddenly applied loads and bursting pressures,

in which trapped stresses are largely avoided, and

which has great resistance to the starting of surface cracks under repeatedly applied loads.

The above and other objects which will be apparent are accomplished by the invention hereinafter described and illustrated in the accompanying drawing which shows in section a tubular structure illustrative of one embodiment of this invention.

As illustrated, the invention is shown in connection with a tubular structure 5 having a wall 6 of hardened metal, the inner portion 1 of which has a hardness of approximately '60 to 62 Rockwell C," and the outer surface 8 of which has a substantially lower degree of hardness, such, for example, as approximately 25 Rockwell C. Between the two extremes the degree of hardness within the wall decreases in a continuous manner from the inner portion 1 to the outer surface 8. In a tube subjected to bursting pressure, the stress to which each part of the tube wall is subjected diminishes from the inside to the outside. In the present invention the decrease in hardness from the inside to the outside parallels the decrease in stress. In other words, the rate of decrease in hardness corresponds generally to the rate of. decrease in the stress from the inside to the outside of the tube. For example, assuming a line 9 -to represent zero hardness,- a dotted line III to represent a hardness of 60 Rockwell C," which is the hardness of the inner portion 1, and a dotted line H to indicate a hardness of approximately 25 Rockwell C, which may be the hardness of the outer surface 8, a substantially flat curve I! would indicate approximately the varying degrees of hardness of the mateterial between the two extremes, and this curve should parallel but not be lower than the stress curve for the tubular structure in question.

One example of the present invention, is a tube having a bore of 4.5 inches, a wall thickness of 1.325 inches, and an outside diameter of 7.15 inches. In such a tube th hardness can vary from 60 Rockwell C at the bore to 25 Rockwell "C at the outer diameter. for example. This tube will withstand the same internal pressure as though hardened uniformly without stress to Rockwell C." At the same time the tube has gained greatly in ductility, machinability, and toughness.

In producing such a tubular structure, the wall 6 is first hardened entirely throughto the highest degree required, for example to a. hardness of approximately 60 Rockwell "C." Preferably, this is done by electro-magnetic induction heating and quenching. Thereafter a drawing heat is applied to the outer surface 8 and a quench is simultaneously applied to the inner bore, for the' purpose of maintaining the original hardness at the inner diameter. The rate of heat input applied to the outer face must be so proportioned to the heat capacity of the tube and so related to the rate of heat outtake on the inner face as to produce a hardness diflerential between the two faces which substantially parallels but is not less than the stress distribution in the tube.

This leaves the material adjacent the bore with a high yield strength and high elastic properties, backed up by material of progressively higher ductility and toughness accompanied by better machinability. The final product of this invention is a heat treated and hardened tube having excellent properties for external machining while at the same time providing for the maximum strength and toughness for such a tubular structure.

It will be obvious that the invention can also be employed to produce a tubular structure having a high degree of hardness at the outer diameter, by drawing the bore while chilling the outer diameter, to produce a tubular structure for use in resisting externally applied pressure.

After the treatment above described a thin layer i4 along the inner bore is drawn by electromagnetic induction heating, for example, to a sufllcient depth to permit machining, which, in the case of a gun tube includes the formation oi rifling grooves i5.

On the completion of the machining operation the machined surface of the inner layer it is hardened by heating and quenching to produce a hardened face IS in the bore, which is then drawn to provide the optimum hardness required for the particular use to which the structure is to be put.

. A tube which is adapted to take the treatment and have imparted to it the characteristics described herein is composed throughout of electromagnetic material which is subject to being hardened by quenching after suitable heating as by electro-magnetic induction means.

magnetic heating and fluid quenching, the wall of which is of one piece, the wall including a relatively thick outer layer comprising almost all of the wall thickness of gradually and approximately uniformly increasing hardness from the outside toward the inside, a relatively thin soft layer immediately inside the hard portion of the outer layer, and a very thin hard layer inside the soft 1 layer forming the interior surface of the bore of the tube. said tube on its interior surface having grooves along its length and raised portions between the grooves and the very thin hard layer covering the exposed inner surfaces of the grooves and raised portions.

2. A metal tube composed throughout of a material which is subject to hardening by electromagnetic heating and fluid quenching, the wall of which is of one piece, the tube being provided with grooves and intervening raised portions in its bore, the wall including a relatively thick outer layer extending from the outside almost to the bottom of the grooves and being of gradually and approximately uniformly increasing hardness from the outside toward the inside, a soft layer just below the bottom of the grooves and Lit below the inside surface of the raised portions, and a relatively very thin hard layer in the bottom of the grooves and on the inside surface of the raised portions.

HOWARD E. SOMES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 460,261 Harvey Sept. 29, 1891 687,612 Davis Nov. 26, 1901 1,097,572 Wales May 19, 1914 1,188,148 Carney et al June 20, 1916 1,395,474 Bray Nov. 1, 1921 2,249,899 Hogg July 22, 1941 2,281,334 Somes Apr. 28, 1942 2,288,033 Somes June 30, 1942 2,292,363 Crawford Aug. 11, 1942 2,293,938 Dunn et a1. Aug. 25, 1942 2,295,272 Somes Sept. 4, 1942 2,316,110 Somes Apr. 6, 1943 FOREIGN PATENTS Number Country Date 24,569 Great Britain of 1894 363,323 Great Britain June 10, 1930 491,939 Great Britain Dec. 3, 1936 472,198 Great Britain Sept. 20, 1937 

